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M. Rotter, B. Stöger:
"RbSbO₃: A Simple Structure with Complex Polytypism";
Crystal Research and Technology (eingeladen), 55 (2020), 5; S. 1900164-1 - 1900164-11.

RbSbO₃ crystallizes in different polytypes composed of trigonal [SbO₃]⁻ and [Rb]⁺ layers, which can appear in two orientations with respect to m_<100> and m_<120>, respectively. The order-disorder (OD) polytype family comprises four polytypes of a maximum degree of order (MDO), of which two are realized in actual crystals: MDO₁ (R-3, c ≈ 19.8 Å, isotypic to ilmenite-like KSbO₃) and MDO₂ (R-3c, c ≈ 39.2 Å, isotypic to AgRuO₃ ). Crystals grown from RbF:Sb₂O₅ in a 2:1 ratio are MDO₁:MDO₂ allotwins, whereas crystals grown from a 12:1 mixture are composed of MDO₂ only. The stacking ambiguity leads to twinning by rotation about <100> or <120>. KSbO₃ crystals grown from KF:Sb₂O₅ are composed of the MDO₁ polytype only. The crystals are fourfold twins owing to stacking faults. A detailed description of the analysis of the diffraction data is given.

allotwinning; order-disorder theory; partial symmetry; polytypism

http://dx.doi.org/10.1002/crat.201900164